Eastern Roman/Greek/Byzantine

Based upon ancient Greek culture and centered on Constantinople, the Eastern Roman Empire was that part of the Old Roman Empire that had remained unconquered by the "barbarian" invasions. They saw themselves as the continuation of the Roman Empire and called themselves "Roman" despite shifts in language, religion, and governmental organization. The term "Byzantine Empire" is a term used by later historians to denote that in many ways the Eastern Roman Empire was fundamentally different from the original Roman Empire after about 650 AD. Their primary language was Greek, they were centered in Asia Minor instead of Europe, they were Christian instead of Pagan, their army was moving to be dominated by cavalry instead of infantry, etc. It is important to note that "Byzantine" was never a term that they used for themselves, they called themselves "Romans" until the fall of Constantinople to the Ottomans in 1453 A.D.
The borders of the Eastern Roman Empire were fluid during the Middle Ages and included southern Italy, all of Asia Minor, and parts of North Africa and the Balkans at their widest extent. The borders shown above are approximately what they were in the mid 10th century during the setting of the books. The Empire was extremely wealthy from all of the trade routes that ran through Constantinople and the "Queen of Cities," as it was called, was the largest city in the world during the 6th and 7th centuries.

Culture

Major language groups and dialects

Greek

Map Citation: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=460636

Eastern Roman (Byzantine) equipment was a blend of eastern and western influences. In many ways, the equipment was similar to the knights of the Frankish Kingdoms but notice the peaked helms and the teardrop-shaped shield. Eastern Roman armies were usually heavy on cavalry with fewer foot soldiers.